Skip to main content
Extension Employees WVU Home

Bacterial Spot of Stone Fruits

Bacterial spot is a disease commonly occurring on stone fruit trees, like peaches, nectarines, apricots, Japanese plums and European plums, throughout the eastern United States. Home gardeners and commercial growers alike are facing this serious problem that can wipe out entire crops in a year with prolonged humid, wet and warm weather. 

One way to minimize the problem is to select cultivars that are tolerant to this disease. Varieties differ in their susceptibility to this disease. For example, Redhaven is resistant, while Babygold 5 appears to be a standard for high susceptibility. Bacterial spot is caused by Xanthomonas campestris, pv. Pruni (Smith) Dye (2). 

Symptoms

Lesions appear on leaves, current season shoots and fruit. Initially, they are just small, water-soaked spots that first show up on the underside of the leaf blade. As the season progresses, they become purplish-black spots that grow and merge, creating irregular spots that will die, dry and fall out, giving the leaf tattering effect. Infected leaves turn yellow and drop off. In severe cases, trees may defoliate early in a season. Similar, sunken areas with purple margins may appear on the young shoots. These can develop into cankers, harboring inoculum for future early infections. Infections on the fruit result in blemishes on the skin, cracking and gumming, diminishing the value and fruit marketability. 

Peach fruit showing bacterial spot symptoms. 
Figure 1. Peach fruit showing bacterial symptoms on fruit.

Bacterial spot symptoms on peach tree symptoms.
Figure 2. Leaf symptoms on leaf tip.

Bacterial spot lesions on leaf of peach tree.
Figure 3. Initial, small leaf lesions 

(Figures 1-3, Courtesy of W. Shane, MSU, SWMREC, Benton Harbor)

Biology 

Bacteria overwinter in the buds, cankers on the twigs or other surfaces that do not exhibit any symptoms. This disease favors cooler weather conditions for its development. In spring, wind and rain carry bacteria, disseminating them onto the young developing shoots, leaves and fruit. Moisture from the fog and dew tend to wash bacteria toward the tips of leaves, causing them to develop brown tips (2). Water presence and congregation is essential for disease infections. 

Heavy rains with water gathering on the leaf tips are ideal conditions for disease infections. Often, there are more symptoms on the side exposed to the driving rain and dominant winds. Oozing cankers and leaf and fruit lesions provide inoculum for ongoing summer infections under warm, humid and wet weather.

Control

The best control is to avoid susceptible and plant resistant varieties. The other consideration is to avoid frost-prone sites and prevent winter injuries that may serve as entry points for this opportunistic pathogen. 

In cases where there are existing older blocks planted with susceptible varieties, maintaining good vigor through slightly higher nitrogen supply to compensate for early defoliation is desirable cultural practice. 

Chemical control is targeting inoculum reduction early in spring. Dormant and early spring applications of copper or copper-based materials will reduce the population of epiphytic bacteria. There is a need for caution whenever we spray copper. To minimize phytotoxicity, it is better to apply lower rates of copper during or following cool weather. Multiple applications may result in phytotoxicity if there has been no rain since the last application and the residual levels are still high. 

Materials showing good efficacy levels are antibiotic, like Mycoshield 17 WP or Oxytetracycline, when applied from petal fall and within three weeks thereafter. The other materials that provide good control are Captan 50 WP in combination with Syllit (Dodine). Caution: Syllit (Dodine) applications may be phytotoxic if combined with, or applied near, solvent formulations of insecticides or sulfur. Do not spray Syllit during the hot temperatures or near harvest. Pre-harvest interval is 15 days (3, 5 Farm Chemical handbook – Global Guide to Crop Protection).

Leaf showing Syllit (Dodine) phytotoxicity.
Figure 4. Syllit (Dodine) phytotoxicity

Leaf showing copper phytotoxicity.
Figure 5. Copper phytotoxicity

(Photos courtesy of  Dr. William Shane, MSU, SWMREC, Benton Harbor, MI)

References: 

  1. USDA/Agricultural Research service (1998): Agriculture handbook Number 714, Handbook of Peach and Nectarine Varieties.
  2. Jones, A., Sutton, T. (1996): Diseases of Tree Fruits in the East
  3. Michigan State Extension Bulletin 154 (2006): Michigan Fruit Management Guide, pp. 62-70
  4. Farm Chemical Handbook – Global Guide to Crop Protection
Author: Mira Bulatovic-Danilovich, WVU Extension Consumer Horticulture Specialist

Last Reviewed: December 2024